The U.S. Centers for Disease Control and Prevention estimates that 300,000 sports-related concussions occur yearly in the U.S., but that number includes only athletes who lost consciousness. Since loss of consciousness is thought to occur in less than 10% of concussions, the actual number is probably closer to 3 million a year. Further, half of these concussions occur in children age 0 to 14, and an addition 38% occur in the age group 15 to 34. Only recently has the extent of sports-related mild traumatic brain injury (MTBI) become known among the general public. In 2010 the University of Wisconsin University published a study in their On Wisconsin magazine that showed everyone who plays football or boxes for 10 years or more suffers permanent brain damage. However, individuals and organizations concerned with protecting sports participants have been pursuing better protective headgear since the early 1940s. Most of such efforts have focused on improving the cushioning inside the helmet's hard plastic shell. Those efforts are ongoing but, to date, no helmet claims to completely preclude concussions.
The laws of Physics limit the effectiveness of internal cushioning because of the limited space insides helmets. Current day football helmets weigh approximately four pounds and contain air cushions approximately one inch thick. The helmets fit over athletes' heads, which weighs, on average, 11 pounds. A sharp blow that causes a 100 g acceleration (g being the acceleration caused by gravity acting on a falling object, or 32.2 feet/sec2) of the helmet cannot be reduced to a safe level with just one inch of padding. Further, the force delivered to the head can be amplified during “rebound” conditions. Such conditions occur when the athlete's head is already moving away from a sharp blow, and is suddenly met with a second force acting opposite to the direction of travel. This is exactly what happens when an athlete's head bounces off the ground. Such a traumatic collision was caught on film in 1960 when Philadelphia Eagle Chuck Bednarik tackled NY Giant Frank Gifford, causing a life-long head injury that caused Frank Gifford to miss the entire next professional football season. Concussions resulting from head collisions are now being treated as a serious issue.
Most concussion studies have focused on measuring head accelerations rather than devising ways of reducing accelerations. Companies and organizations have developed small accelerometers that players may ware to record the accelerations (linear and rotational) experienced during contact. Such data is useful in determining the acceleration levels that produce concussions, currently believed to be between 100 g and 150 g.
The National Operating Committee on Standards for Athletic Equipment (NOCSAE) has meticulously developed methodologies to test the ability of football headgear to limit head accelerations. Their principal test for football helmets consists of dropping a helmeted Headform (i.e. simulated head) onto a half inch thick polyurethane pad that measures the deceleration of the helmeted Headform. The tests prescribe a variety of impact velocities with the helmet oriented in different positions. Further, the NOCSAE has developed a measure of the severity of impacts, called the Severity Index (SI). The SI is defined as the integral of the instantaneous acceleration, A (expressed as multiples of the gravitational acceleration, g) raised to the 2.5 power, measured over the interval when A equals or exceeds 4.0. Mathematically, this becomes:
  SI  =            ∫              t        1                    t        2              ⁢                  A        2.5            ⁢      dt      
where SI has units of seconds.
The NOCSAE prescribes limits on SI as a function of impact speed and point of impact on the helmet. As such, the Severity Index provides an objective measure of the protective value of helmets. For example, NOCSAE prescribes that the SI of a 17.94 foot/sec impact shall not exceed 1200 for any helmet impact orientation. (NOCSAE cautions that the 1200 SI value is just a threshold, stating “There is no measurable difference in safety of helmets with scores below the 1200 SI threshold. For example, a helmet scoring 400 SI isn't more likely to reduce injury than one scoring 800 SI. Once the SI value gets below approximately 800 to 900, the change to the risk of injury is essentially immeasurable.”)
While prior designs that only employ cushioning material on the inside of the helmet can meet NOCSAE requirements, they cannot guarantee protection against concussions. Accordingly, investigators have looked at adding cushioning material on the outside of the helmet. In particular, Alfred Pettersen (US Patent 20150000013A1) invented an exterior sport helmet pad that was formed to fit over the helmet, and was held in place by internal contact pressure. Although such a cushioning device may provide some additional protection, it would be prohibitively expensive because a separate mold would be required for each size of each helmet design. Further, covering the entire outer surface of the helmet with extra padding could make the helmet excessively heavy, and thereby adversely affect athletic performance. In addition, Pettersen's conclusion that a pad thickness of only 0.5 to 0.75 inches thick was sufficient to mitigate concussions was unfounded because his tests did not conform to NOCSAE specifications. In particular, Pettersen's top impact speed was 8.97 feet/sec, which is below the minimum test speed of 11.34 feet/sec prescribed NOCSAE, and well below the NOCSAE maximum test speed of 17.94 feet/sec. Finally, Pettersen did not report the Severity Index for any test (as required by NOCSAE), but rather reported the amount that his external padding reduced the peak acceleration. Although Pettersen described the NOCSAE helmet tests within his patent, he gave no indication that any such tests were actually performed as specified.
Cannon et al. (U.S. patent application Ser. No. 15/156,537) developed an analytical model of the dynamics governing helmet impact which could be used to methodically design a cushioning system capable of mitigating concussions. Their analysis showed that external cushions having thicknesses between 0.5 inches and 1.0 inches can reduce the Severity Index an order of magnitude below the NOCSAE threshold of 1200, provided the elastic modulus (E) of the cushions lay in the range between 120 psi to 240 psi. Several commercially-available polymer foam materials have elastic properties that lie within this range and therefore can be used to construct cushions to protect the hard outer shells of headgear. In particular, open cell foam materials are preferable to closed cell foam materials because open cell foams dissipate more energy than closed cell foams. (In fact, the equations developed by Cannon et al. show that closed-cell foams and air cushions dissipate less energy than a football helmet's hard outer shell, thereby resulting in more rebound after impact. This undesirable effect was confirmed in physical tests.)
Since it has been established that energy-absorbing cushions applied to the hard outer shells of headgear can reduce the severity of accelerations transmitted to the wearer's head, the remaining challenge is optimize the cushion design and installation methods to maximize performance and acceptance, at an affordable cost. Cannon et al. (U.S. patent application Ser. No. 15/156,537) devised a system of cushions to protect the hard outer shell of headgear that was inexpensive to fabricate and could be installed onto any model and size of headgear. Although the system completely protected the crown of the headgear, it did not provide continuous 360 degree protection around the sides of the headgear. This is significant because blows can come from any direction during athletic competition. Also, the Cannon et al. system relied upon hooks and clips to affix the cushions to the headgear. This can be an issue because the thickness of the hard outer shell of headgear varies along its edge, thereby necessitating different size clips and hooks to attach the cushions to the headgear. This is particularly challenging for the rear edge of the hard outer shell which is typically covered by a rear rubber pad that protects the back of the wearer's neck. The presence of the rear rubber pad makes it difficult to securely attach a clip or hook to the rear of the hard outer shell without disturbing the rear rubber pad. Also, the presence of a hard clip or hook in the vicinity of the wearer's neck can constitute a safety hazard. Finally, it's possible for clips and hooks to be dislodged by violet blows to the headgear.
The present invention builds on the work of Cannon et al. by devising a system of cushions that provide full 360 degree protection around the circumference of the headgear, and which can be installed without using clips, hooks, buckles, or adhesives.